It has been proposed a process for producing 1,4-diazabicyclo-(2,2,2)-octane by reacting an alkylene polyamine as a starting material on a catalyst such as a metal phosphate, a silica-alumina type compound in gaseous phase at 250.degree. to 550.degree. C.
In these processes, various amines including piperazine and alkyl piperazines as by-products are produced together with the object compound of 1,4-diazabicyclo-(2,2,2)-octane.
Accordingly, 1,4-diazabicyclo-(2,2,2)-octane is obtained by repeating separations such as distillation, cooling and drying from the resulting amines mixture.
However, alkyl pyrazines such as 2-ethyl-3-methyl pyrazine, 2-ethyl-6-methyl pyrazine and 1-propyl pyrazine among the amines mixture, have boiling points similar to the boiling point of 1,4-diazabicyclo-(2,2,2)-octane whereby it is difficult to obtain a pure 1,4-diazabicyclo-(2,2,2)-octane by a simple distillation.
These alkyl pyrazines remain in a process solution including 1,4-diazabicyclo-(2,2,2)-octane to accumulate the alkyl pyrazines in the process solution. Sometimes, it is necessary to stop the operation whereby the process for producing 1,4-diazabicyclo-(2,2,2)-octane is interrupted.
In the process for producing 1,4-diazabicyclo-(2,2,2)-octane, a separation of the alkyl pyrazines from the process solution is important and indispensable to obtain 1,4-diazabicyclo-(2,2,2)-octane having high purity and to overcome a trouble in the process. Moreover, it is desired to develop a separation of the alkyl pyrazines so as to decrease a loss of 1,4-diazabicyclo-(2,2,2)-octane.